Context transition issues

Here's what I think is going on with your Test 2:

Product[Test 2]=CALCULATE(ALL(’Product’[ProductKey]))

CALCULATE only requires one input, ALL (Product [ProductKey]) in your example.  So what happens if we create a table just off of that:

  ALL and VALUES will return the same table in this example.  Back to the formula :

Test 2 (CALC just ALL) = CALCULATE(ALL( 'Just product Keys'[ProductKey]))

We now know that the ALL returns a table of all the product keys.  So what does it do with them?!  CALCULATE takes the row you are in (have row context since you are in a calculated column) and transitions that from a row context to a filter context.  In the first row of the example, we have Product Key =1 and then that is compared to the ALL product key, which is then why you just get the product key in this calculated column.  Long and short of it is that where the ALL is used in this calculated column does not remove any filters ( since it is not used as filter input), just returns a column without any filters, and then the current row is used as a filter.  

So what happens in your test 3??

Test 3 (CALC, COUNTROWS, ALL) = 
 CALCULATE(
     COUNTROWS(
         ALL('Just product Keys'[ProductKey])
     )
 )

Now ALL is being used differently.  ALL really has two functions: Ignore Filters and Return a table.  In this situation it is being used to ignore the filer context ( the row product key in our example) and return the entire table to be be counted.  That is why it works without CALCULATE, beacuse its not doing anything.

Then what about test 4?

Test 4 = 
	CALCULATE(
		COUNTROWS(
			VALUES('Just product Keys'[ProductKey])
		)
	)

Here Values is only able to return a table, it has nothing to do with ingoring filters like ALL.  So we end up with 1 for each row since here calculated transforms the current row context into a filter context which is then applied to the Values.  Since these are Keys, no dupes, the answer is one for each row.  If you remove the CALCULATE from this one you end up with the entire table since no context transition takes place.

And just for fun (well I guess fun, not so sure at this point..) what if we mix FILTER, ALL, COUNTROWS?

Column = 
COUNTROWS(
    FILTER (
	    ALL( DimProduct[ProductKey]),
			DimProduct[ProductKey]<= 10 
		)
)

The general way CALCULATE is used is :

=CALCULATE(
[Measure],
Some sort of filter)

Filters could be simple such as Product[Color] = "Red" or more complex using FILTER:
FILTER( ALL ( Product[Color]))
		

This can be a pretty complex topic, and I admit I struggled to say why this was happeninng, I understood it just hard to put into words.  I think it will just take some time in developing in DAX and seeing the theory play out in reality.  But also need to keep up with the theory.  Hope this helps and not made it more confusing:smileyfrustrated: